Appendicitis

Written By: Charmaine Gregory
University of Michigan & St.Joseph Mercy Hospital, Ann Arbor, Michigan

Edited By: David Gordon, MD
Duke University, Durham, North Carolina

Objectives

Upon completion of this module, the learner will be able to:

  • Describe the classic signs and symptoms of appendicitis
  • Discuss the role of the white blood cell count and C-reactive protein in the diagnosis of appendicitis
  • Discuss the advantages and limitations of different imaging modalities in the evaluation of appendicitis
  • Discuss the management of appendicitis

Appendicitis is the most common emergent surgical condition of the abdomen in the United States. While its peak incidence is during the second and third decades of life, it is a disease that occurs across the entire age spectrum. Timely diagnosis and treatment of appendicitis are critical in reducing the risk of perforation which is associated with increased morbidity and mortality. The mortality rate of appendicitis escalates from less than 1% in non-perforated cases to 5% or more in perforated cases. Given its prevalence and the consequences of missed or delayed diagnosis, it is paramount that appendicitis be considered in the evaluation of any patient with undifferentiated abdominal pain.

Classic Presentation

History

The classic presentation for appendicitis involves the onset of vague epigastric or periumbilical pain followed by anorexia, nausea or vomiting and the migration of pain to the right lower quadrant (RLQ). Owing in part, however, to the large variability in the location of the appendix, only one-half to two-thirds of patients will present in this manner. For example, retrocecal appendicitis may present with vague and poorly localized pain while pelvic appendicitis can cause midline or left-sided abdominal pain.

The historical factors with the highest predictive value for appendicitis are RLQ pain (positive LR of 7.31-8.46), migration of pain from the periumbilical region to the RLQ (positive LR of 3.18), and pain before vomiting (positive LR of 2.76). Anorexia is the most common associated symptom with a sensitivity of 68% but lacks predictive value as it is commonly seen in other abdominal conditions. A history of similar pain does not exclude appendicitis but lowers the likelihood and should prompt consideration of alternative diagnoses.

It is important to recognize that symptoms commonly associated with other disease processes can also be seen with appendicitis. Constipation or diarrhea (especially in children) can occur and should be not used in isolation to exclude appendicitis. Similarly, irritative voiding symptoms (e.g., dysuria or frequency) can occur when an inflamed appendix is lying near the ureter or bladder.

Physical Exam

Abdominal rigidity (involuntary guarding) is the sign with the highest predictive value for appendicitis (positive LR of 3.76). Fever is typically absent during the initial onset of pain but commonly develops within the first 24 hours. Overall, fever has poor predictive value for appendicitis. The following signs have been associated with appendicitis but have low predictive value:

Signs in Appendicitis
SignDescriptionImplicationImages
PsoasPain with passive extension of right hip or with active flexion of right hip against resistanceRetrocecal appendix
ObturatorPain with passive internal rotation of right hipPelvic appendix
RovsigPain in RLQ with palpation of LLQ

Special Populations

Certain patient populations present atypically for appendicitis and are thus at high risk of being misdiagnosed. Infants and young children (age less than 5) tend not to be diagnosed until perforation has occurred. In addition to limited communication skills, young children pose a diagnostic challenge due the non-specific nature of their symptoms (i.e., abdominal pain, fever, and vomiting) as well as their high prevalence of atypical symptoms such as diarrhea, grunting, or a limp. Diarrhea was reported in 41% of cases of appendicitis in children less than 3 years old with gastroenteritis not surprisingly being the most common misdiagnosis.

Other high risk populations include the elderly who often present late in the disease course, may have more subtle signs and symptoms, and require a broad differential diagnosis for abdominal pain. Pregnant patients may have an atypical presentation due to displacement of the appendix by the gravid uterus. Patients on steroids or other immunosuppressants may have a blunted inflammatory response and thus may not develop rigidity or rebound tenderness. It is paramount that the physician maintains a high index of suspicion for appendicitis in these patient populations.

Diagnostic Testing

Laboratory studies

There is not a single laboratory study specific for appendicitis. While 70-90 percent of patients will have a white blood count (WBC) greater than 10,000 cells/mm3, there are also many other abdominal and pelvic conditions that can cause a leukocytosis. Overall, the WBC has not been found to have strong predictive value in appendicitis and should not be used alone to rule in or rule out the disease.

The ability of C-reactive protein (CRP) to exclude appendicitis as an isolated marker or in combination with the WBC has been investigated. There are retrospective studies that indicate a high negative predictive value when normal values are obtained for CRP, WBC, and neutrophil count. Overall, more prospective data on CRP is needed to establish its role in the evaluation of appendicitis.

Urinalysis is important for determining the pregnancy status in childbearing females and ruling out urinary tract infection. However, there is a possibility of a microscopic pyuria or hematuria caused by the proximity of the appendix to the ureter and bladder in acute appendicitis. The presence of more than 20 WBC per high-power field in the urine is more suggestive of a urinary tract disorder.

Ultrasound

Ultrasound is 75 to 90% sensitive for the diagnosis of appendicitis. The ultrasonographic findings suggestive of appendicitis include: a noncompressible lumen, a diameter greater than 6mm (98% sensitive, some centers use 7mm), absence of gas in the lumen, appendicoliths, and a thickened wall. Occasionally, inflammatory changes can be detected in the surrounding tissue to aid in the diagnosis. The use of Doppler as an adjunct - especially when the appendiceal measurements are equivocal - can reveal increased vascularity in and around the acutely inflamed appendix. A positive Doppler finding has a reported sensitivity of about 87% but blood flow decreases in advanced inflammation (intraluminal pressures exceed perfusion pressures), and Doppler signal is diminished when the appendix is close to necrosis or gangrenous.

The accuracy of ultrasound for appendicitis improves when the patient is able to indicate the area of maximal tenderness, but its negative predictive value is markedly diminished if the appendix is not visualized. Furthermore, false negatives are more likely in cases of perforated appendicitis (where the appendix is usually decompressed), and inconclusive studies more common in those with significant bowel gas and obesity.

Ultrasound offers the advantage of avoiding exposure to ionizing radiation and is thus the initial imaging study of choice in pediatrics and pregnant patients. It is also useful in women of childbearing age in whom gynecological causes of right lower abdominal pain are also being explored.

CT

CT has become the imaging study of choice for evaluating acute appendicitis in adults. There have been several prospective studies that have demonstrated the superiority of CT over ultrasound in diagnosing appendicitis. In these comparison studies, the sensitivity of CT was found to be 95 to 96 percent versus 76 to 87% sensitivity for ultrasound. CT has also been shown to be more useful than ultrasound in detecting an alternative diagnosis in patients who did not have appendicitis. CT findings specific for appendicitis include an enlarged appendix (> 6mm in outer diameter), enhancement of the appendiceal wall, lack of opacification of an enlarged appendix, an appendicolith, and periappendiceal stranding.

There is some ambiguity about the importance of contrast material in maximizing the diagnostic accuracy of current helical CT for appendicitis. IV contrast is noted to have the advantage of highlighting inflammation of the appendix and surrounding tissues but carries the risk of nephrotoxicity and allergic reactions. PO contrast can facilitate the differentiation of the appendix from surrounding structures but can be difficult to administer in patients with nausea and vomiting and can lead to a delay in diagnosis due to the need to ingest oral contrast over several hours. The use of rectal contrast only has been found to be highly accurate but may pose problems with patient comfort. Studies have reported the sensitivity of a noncontrast CT for appendicitis to be 91-96%, but the skill level and experience of the radiologist must be considered. Another important consideration that would favor the use of contrast is the improved sensitivity for other possible intra-abdominal pathology that could be the cause of the patient's pain.

Click to view CT scan of Appendicitis
Dilated appendix with periappendical stranding
Coronal Reconstruction of CT showing dilated appendix with periappendical stranding
Dilated appendix measured at 14 mm. Surrounding free fluid and fat stranding also present
Multiple appendicoliths
Coronal Reconstuction of CT showing enlarged appendix with surrounding free fluid and stranding

Plain radiography

In general, plain radiographs are not useful in making the diagnosis of appendicitis. An opaque fecalith can be identified in the right lower quadrant in less than 5% of patients.

Magnetic Resonance Imaging

MRI has limited use in the diagnosis of appendicitis. Although MRI avoids ionizing radiation, it has several disadvantages including cost, limited availability on an emergent basis, and study length. Some institutions reserve MRI for pregnant patients in whom ultrasound was inconclusive. Gadolinium crosses the placenta and enters the fetal circulation, where it remains for an indefinite amount of time (it is excreted by the fetal kidney then swallowed by the fetus in amniotic fluid). Mutagenic effects of gadolinium have been demonstrated in animal studies, but no evidence for tetratogenic or mutagenic effects have been noted in humans so far. The use of gadolinium is to be avoided in the first trimester.

T2-weighted images best depict the findings of acute appendicitis. These findings include filling of the lumen of the appendix with high intensity, thickening of the appendix wall with high intensity, increased intensity of periappendiceal tissue and marked enhancement of the appendix wall on fat suppression. On MRI, the abnormal appendix is distended to greater than 6 mm and increased wall thickness of more than 2 mm.

How do I make the diagnosis?

Patients with the classic presentation for appendicitis involving acute abdominal pain (typically less than 48hours) that has migrated from the umbilicus to RLQ in association with RLQ tenderness may not require any further diagnostic work-up. In women it is important to make sure gynecologic disease has been appropriately considered, but otherwise a surgical consult can be immediately obtained for an appendectomy.

Patients with an equivocal presentation for suspected appendicitis will typically require diagnostic imaging. A WBC is usually obtained as part of the evaluation but the absence of a leukocytosis should not preclude the use of imaging in the setting of high clinical concern. CT is the preferred imaging modality given its high sensitivity for appendicitis as well as ability to identify perforated appendicitis, abscesses, and alternative diagnoses. Ultrasound will be the first imaging study of choice in children, pregnant females, and young women with suspected gynecological disease. Observation and serial exams provides an option in pregnant women and children with equivocal ultrasound results as well as in low-risk patients as a means of avoiding exposure to ionizing radiation.

The diagnosis of appendicitis can be elusive due to several confounding factors (varied location of pain, age of patient, and atypical signs and symptoms), so maintaining a high clinical suspicion is imperative.

Treatment

The treatment of choice for acute appendicitis is appendectomy. Antibiotics for surgical wound prophylaxis should be started once the diagnosis is made with ampicillin/sulbactam or cefoxitin as examples of appropriate choices. In the case of a pre-surgical identification of a perforated appendix, broader spectrum antibiotics are necessary. In some cases, delayed appendectomy status post image-guided percutaneous drainage and prolonged antibiotics is an appropriate management plan.

Disposition

Pearls and Pitfalls

Selected References